Magnetic resonance imaging apparatus

A review of the theory, technology, and use of radio frequency (RF) coils for small-animal MRI is presented. It includes a brief overview of MR signal-to-noise (S/N) analysis and discussions of the various coils commonly used in small-animal MR: surface coils, linear volume coils, birdcages, and their derivatives. The scope is limited to mid-range coils, i.e. coils where the product (fd) of the frequency f and the coil diameter d is in the range 2-30 MHz-m. Common applications include mouse brain and body coils from 125 to 750 MHz, rat body coils up to 500 MHz, and small surface coils at all fields. In this regime, all the sources of loss (coil, capacitor, sample, shield, and transmission lines) are important. All such losses may be accurately captured in some modern full-wave 3D electromagnetics software, and new simulation results are presented for a selection of surface coils using Microwave Studio 2006 by Computer Simulation Technology, showing the dramatic importance of the "lift-off effect". Standard linear circuit simulators have been shown to be useful in optimization of complex coil tuning and matching circuits. There appears to be considerable potential for trading S/N for speed using phased arrays, especially for a larger field of view. Circuit simulators are shown to be useful for optimal mismatching of ultra-low-noise preamps based on the enhancement-mode pseudomorphic high-electron-mobility transistor for optimal coil decoupling in phased arrays. Cryogenically cooled RF coils are shown to offer considerable opportunity for future gains in S/N in smaller samples.

Radio frequency coil technology for small-animal MRI.

A review of the theory, technology, and use of radio frequency (RF) coils for small-animal MRI is presented. It includes a brief overview of MR signal-to-noise (S/N) analysis and discussions of the various coils commonly used in small-animal MR: surface coils, linear volume coils, birdcages, and their derivatives. The scope is limited to mid-range coils, i.e. coils where the product (fd) of the frequency f and the coil diameterd is in the range 2-30MHz-m. Common applications include mouse brain and body coils from 125 to 750MHz, rat body coils up to 500MHz, and small surface coils at all fields. In this regime, all the sources of loss (coil, capacitor, sample, shield, and transmission lines) are important. All such losses may be accurately captured in some modern full-wave 3D electromagnetics software, and new simulation results are presented for a selection of surface coils using Microwave Studio 2006 by Computer Simulation Technology, showing the dramatic importance of the 'lift-off effect'. Standard linear circuit simulators have been shown to be useful in optimization of complex coil tuning and matching circuits. There appears to be considerable potential for trading S/N for speed using phased arrays, especially for a larger field of view. Circuit simulators are shown to be useful for optimal mismatching of ultra-low-noise preamps based on the enhancement-mode pseudomorphic high-electron-mobility transistor for optimal coil decoupling in phased arrays. Cryogenically cooled RF coils are shown to offer considerable opportunity for future gains in S/N in smaller samples. Copyright # 2007 John Wiley & Sons, Ltd.

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Review Article Radio frequency coil technology for small-animal MRI

This invention discloses a method and apparatus to deliver medical devices to targeted locations within human tissues using imaging data. The method enables the target location to be obtained from one imaging system, followed by the use of a second imaging system to verify the final position of the device. In particular, the invention discloses a method based on the initial identification of tissue targets using MR imaging, followed by the use of ultrasound imaging to verify and monitor accurate needle positioning. The invention can be used for acquiring biopsy samples to determine the grade and stage of cancer in various tissues including the brain, breast, abdomen, spine, liver, and kidney. The method is also useful for delivery of markers to a specific site to facilitate surgical removal of diseased tissue, or for the targeted delivery of applicators that destroy diseased tissues in-situ.

Hybrid imaging method to monitor medical device delivery and patient support for use in the method

Apparatus and method for using radio frequency coil systems for magnetic resonance imaging within an open architecture apparatus is provided. The MRI coil system includes a support structure with an open architecture in which secondary support structures, compression systems and plates containing RF coil systems may be introduced. These structures and RF coils can be moved relative to the patient, or removed entirely from the system. In one embodiment the system consists of a tabletop coil system, while another embodiment consists of a dedicated stretcher design.

Open architecture imaging apparatus and coil system for magnetic resonance imaging

A floating shield current trap provides first and second concentric tubular conductors electrically connected to provide a resonance-induced high impedance of current flow in a path consisting of the inner and outer conductors and their junctions thereby suppressing coupled current flow on a shield of a conductor contained within the first inner tubular conductor.

Floating radio frequency trap for shield currents

A decoupling circuit for decoupling an local coil during the application of an RF excitation signal in a magnetic resonance imaging system includes a passive switching circuit for switching an inductor in parallel with a capacitive circuit in the local coil, and a discharge circuit for discharging residual currents from the circuit, therefore allowing for rapid coupling and decoupling of the local coil

Decoupling circuit for magnetic resonance imaging local coils

A modular lower coil provides for a head, a vascular and, a thoracic/lumbar element that may interfit or be separated to provide individual imaging of these areas or a combined imaging region stretching from the head to the lower spine. A switch box allows individual ones of these elements to be connected to the MRI machine if necessary because of a limitation of inputs to the machine and provides for decoupling currents to minimize interference between the coil elements when one element is being used.

Modular local coil set for magnetic resonance imaging

A head coil for magnetic resonance imaging may be shortened longitudinally to provide for better access by a patient. Extension of the coil may be performed after the positioning of the patient's head significantly simplifying patient positioning with respect to the coil. A portion of a conductor support sliding over the patient's head may be removable to allow endotracheal tubes or the like to remain undisturbed.

Retracting mri head coil

A local coil for magnetic resonance imaging employs a loop divided by a shunting conductor which reduces sensitivity and field strength at one end of the loop to provide improved homogeneity for different coil configurations.

Loop MRI coil with improved homogeneity

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